On June 7, 2019 US EPA issued a guidance document clarifying its interpretation of provisions of Section 401 of the Clean Water Act (CWA). Under Section 401, a federal agency may not issue a permit or license to conduct any activity that may result in any discharge into the waters of the United States unless a state or authorized tribe where the discharge would originate issues a 401 water quality certification verifying compliance with existing water quality requirements or waives the certification requirement. In its guidance document, EPA states that state certifications should be limited to water quality issues and standards described in the Clean Water Act. The document also limits how much time states have to make their certification by clarifying that the clock for determinations on applications begins when state receives it and cannot be stopped even if applicants do not respond to state requests for more information as has occurred in the past. While this guidance document is merely interpretive and does not have the force of law, it does send state’s a message that if not followed, they should expect litigation on its basis. As a result, state’s enforcement and regulatory abilities over certain projects are likely less flexible.